There is, of course, one significant problem, which is that the leader of the band of immortals isn’t actually immortal anymore. Andy is fortunate to discover that her healing abilities are gone after receiving a non-lethal injury, and she certainly seems like she is in good shape at the very end of The Old Guard, but every mission going forward will come with a risk that didn’t previously exist in such a concrete way. She’s clearly still an important asset within the group, as her experience as potentially the longest-living being on Earth is invaluable, but tactics and strategy will need to change in battle.
The team could likely function like this for a very long time, but then there is also that other lingering story hanging out there…